Power-saving operation of data carriers has become known, for example, with the object of German patent 103 30 451 B3, in which a wake-up command is sent from a control device to a data carrier, so that the latter goes into an awake state and is ready to receive corresponding signals from the control device. With this, there is the advantage that the data carrier consumes relatively high current only when it has in fact received the wake-up command.
However, a disadvantage of this known arrangement is that the wake-up command always puts the data carrier into an awake state immediately, and thus makes it ready to receive the corresponding signals of the control device. In this connection, it is presumed, in the state of the art, that the length of the wake-up signal is longer than the so-called “sniff period.” “Sniff period” is understood to mean pulse-wise wake-up, and a pulse-wise reception mode of the RFID data carrier.
In accordance with this requirement, it is necessary that the length of the wake-up signal is longer than a sniff period. In this way, it is ensured that one wake-up signal, in each instance, can be received during the pulse-wise reception operation.
The fact that after expiration of the wake-up signal, the command itself is also transmitted at the end of the wake-up signal, is also part of the state of the art. During this time, in the state of the art, the data carrier has to be in reception readiness mode, and this consumes unnecessary power. In other words, it must remain in the awake state during the entire wake-up command and even afterward, during transmission of the actual command, and this unnecessarily uses battery power.